They're still just a couple of medium-bore defensive handguns chambered in a couple of the more popularly used service-type calibers.

Yes, unless your fiancee is a skilled, well-practiced and experienced shooter, she's likely to feel the G26 offers her a more controllable shooting experience. Maybe still even if she is an experienced shooter. Some folks simply prefer the G26 to the G27 when it comes to felt recoil and how it's perceived, as well as overall recoil management. Just depends.

I own both, myself. I've run a fair number of rounds through each subcompact (meaning more than 12K rounds of each caliber in the subcompact Glock 9/.40 models).

Some other thoughts I recently posted in a similar thread elsewhere in this forum:

Perception of felt recoil is very subjective and can easily vary among shooters, or even be experienced differently by the same shooter on different days, even using the same guns/ammo. Just depends.

FWIW, I can generally distinguish between standard pressure, +P & +P+ in my various 9's, as long as I'm going slowly and paying attention, trying to notice the difference while engaged in slow-fire 'target type' shooting. That's probably because I'm relaxed, not distracted by expecting to be shot by the paper target and I'm expecting to be able to distinguish the difference.

However, once I start running the guns in fast-paced, demanding courses-of-fire I don't often notice the difference. My attention is more focused on identifying designated threat targets from non-threat targets, doing whatever drills are being required during the various courses of fire, remaining aware of loading as needed (slide-lock) or by choice, using barricades/cover, moving & shooting, shooting while moving, doing both 1 & 2-handed shooting from either hand, etc. Too busy to try and distinguish the level of felt recoil.

That said, I can usually notice a difference between shooting my similarly sized .40's and 9's, even when shooting 124gr +P & 127gr +P+ loads in my 9's.

Problematic? Not so much. Then again, I've fired some ten's of thousands of rounds of .40 since I bought my first one back about 2000 (I presently own 5), and was later issued a couple of them at different times.

I look at it as a training & familiarity issue.

I've worked with some folks who are very sensitive and aware of the differences in felt recoil between most 9's & .40's, especially when we were using +P+ loads for a bit, and yet other folks weren't as aware of the difference. Just depended on the individual, and it wasn't always predictable by their expressed level of interest in shooting, their experience or their preference for any particular caliber.

Even when running folks who claimed they couldn't notice a difference between 9/.40 through various drills, though, sometimes the timer would tell a different story, as they'd often be faster with the 9's, or at least less likely to anticipate recoil and miss shots.

One thing I've noticed over the years since I've been shooting .40's, however, is that the more I work with my .40's, I not only do better with them, but I do better with my 9's, as well.

A case in point is my 4040PD. It's essentially a 3913 made using a Scandium aluminum frame (for greater strength than the standard aluminum alloy), but chambered in .40 S&W.

When I first bought it several years ago I felt it had significantly more recoil than my 3913, even when shooting +P+ loads (115gr & 127gr) in my 3913. That made sense to me at the time, as I'd also felt my 4013TSW had more felt recoil than my issued 6906 (used with 127gr +P+ duty loads). I sort of sidelined it in my safe, shooting my other .40's.

Now, just the other day I decided to pull it from the safe and do some work with it while working a range session. I immediately noticed two things during the first couple of mag loads while doing a qual course-of-fire "cold" (no "warm up" after not having fired the gun for a few years).

The gun exhibited excellent accuracy & controllability from the very first DA shot ... and the felt recoil just didn't seem as significantly greater than that of my 3913 (when I was recently using it with some +P & +P+ loads) as it did several years ago. Not like I remembered. Go figure.

Something's changed in the last few years, and it probably wasn't the gun or the ammo.

I guess the thing is that I can't presume to provide a definitive "answer" for anyone other than myself, and even that seems to be a bit variable over time, at least to some degree.

If you have the opportunity to participate in a local IDPA event, consider running through one with guns in both calibers and seeing what you think about them in circumstances involving other than slow-fire target shooting from a static firing line or bench position.